Don't it always seem to go, that you don't know what you’ve got ‘til it’s gone. --- Joni Mitchell
You can't get what you want till you know what you want. --- Joe Jackson
Joni and Joe are both correct but there's another aspect: You can't tell what you want until you know what's available. Let's explore this with a concrete example.
This podcast accompanies a blog post at Riscario Insider: http://blog.riscario.com/2009/10/why-you-cant-know-what-you-want.html